Backward Incompatible Changes

Although most existing PHP 4 code should work without changes, you should pay attention to the following backward incompatible changes:

There are some new reserved keywords.
strrpos() and strripos() now use the entire string as a needle.
Illegal use of string offsets causes E_ERROR instead of E_WARNING. An example illegal use is: $str = 'abc'; unset($str[0]);.
array_merge() was changed to accept only arrays. If a non-array variable is passed, a E_WARNING will be thrown for every such parameter. Be careful because your code may start emitting E_WARNING out of the blue.
PATH_TRANSLATED server variable is no longer set implicitly under Apache2 SAPI in contrast to the situation in PHP 4, where it is set to the same value as the SCRIPT_FILENAME server variable when it is not populated by Apache. This change was made to comply with the » CGI/1.1 specification. Please refer to » bug #23610 for further information, and see also the $_SERVER['PATH_TRANSLATED'] description in the manual. This issue also affects PHP versions >= 4.3.2.
The T_ML_COMMENT constant is no longer defined by the Tokenizer extension. If error_reporting is set to E_ALL, PHP will generate a notice. Although the T_ML_COMMENT was never used at all, it was defined in PHP 4. In both PHP 4 and PHP 5 // and /* */ are resolved as the T_COMMENT constant. However the PHPDoc style comments /** */, which starting PHP 5 are parsed by PHP, are recognized as T_DOC_COMMENT.
$_SERVER should be populated with argc and argv if variables_order includes "S". If you have specifically configured your system to not create $_SERVER, then of course it shouldn't be there. The change was to always make argc and argv available in the CLI version regardless of the variables_order setting. As in, the CLI version will now always populate the global $argc and $argv variables.
An object with no properties is no longer considered "empty".
In some cases classes must be declared before use. It only happens if some of the new features of PHP 5 (such as interfaces) are used. Otherwise the behaviour is the old.
get_class(), get_parent_class() and get_class_methods() now return the name of the classes/methods as they were declared (case-sensitive) which may lead to problems in older scripts that rely on the previous behaviour (the class/method name was always returned lowercased). A possible solution is to search for those functions in all your scripts and use strtolower(). This case sensitivity change also applies to the magical predefined constants __CLASS__, __METHOD__, and __FUNCTION__. The values are returned exactly as they're declared (case-sensitive).
ip2long() now returns FALSE when an invalid IP address is passed as argument to the function, and no longer -1.
If there are functions defined in the included file, they can be used in the main file independent if they are before return or after. If the file is included twice, PHP 5 issues fatal error because functions were already declared, while PHP 4 doesn't complain about it. It is recommended to use include_once instead of checking if the file was already included and conditionally return inside the included file.
include_once and require_once first normalize the path of included file on Windows so that including A.php and a.php include the file just once.
Passing an array to a function by value no longer resets the array's internal pointer for array accesses made within the function. In other words, in PHP 4 when you passed an array to a function, its internal pointer inside the function would be reset, while in PHP 5, when you pass an array to a function, its array pointer within the function will be wherever it was when the array was passed to the function.

Example #1 strrpos() and strripos() now use the entire string as a needle


<?php
var_dump(strrpos('ABCDEF','DEF')); //int(3)

var_dump(strrpos('ABCDEF','DAF')); //bool(false)
?>

Example #2 An object with no properties is no longer considered "empty"


<?php
class test { }
$t = new test();

var_dump(empty($t)); // echo bool(false)

if ($t) {
    // Will be executed
}
?>

Example #3 In some cases classes must be declared before used


<?php

//works with no errors:
$a = new a();
class a {
}


//throws an error:
$a = new b();

interface c{
}
class b implements c {
} 

?>

User Contributed Notes

john.g

11 years ago


PATH_TRANSLATED is handy when using Apache's ModRewrite engine, as it gives you the name and path of the resulting file rather than the one that was requested by the user. Since PHP 5.0 and Apache 2 no longer support this variable, I created a workaround by adding an environment variable to my ModRewrite command:

Original:
RewriteRule ^/test/(.*)\.php(.*) /test/prefix_$1.php$2

Adjusted:
RewriteRule ^/test/(.*)\.php(.*) /test/prefix_$1.php$2 [E=TARGET:prefix_$1.php]

I could then find out the resulting file name through the super global $_ENV, for instance:

<?php
echo "The actual filename is ".$_ENV['REDIRECT_TARGET'];
?>

Note: The "REDIRECT_" prefix appears to be allocated automatically by ModRewrite.

Anonymous

10 years ago


is_a have been deprecated. You can simply replace all occurences with the new instanceOf operator, although this will break backwards-compatibility with php4.

michael dot darmousseh at gmail dot com

6 years ago


Hack way to fix the array_merge problem so that it works with your existing php4 code



<?php

function array_merge5()

{

    $args = func_get_args();

    foreach($args as $key=>$arg)

        $args[$key] = (array) $arg;

    return call_user_func_array("array_merge", $args);

}

?>



just put it somewhere completely accessible to your codebase and change all of your calls to array_merge to array_merge5.

nami

8 years ago


addition of the note on 07-Sep-2004 06:40



if you write down your code like this PHP5 will just work fine:



<?php

     $array_1 = array('key1'=>'oranges','key2'=>'apples');

     $array_2 = array('key3'=>'pears','key4'=>'tomatoes');

     $array_3 = array();

     $arr_gemerged = array_merge($array_1,$array_2,$array_3);

     echo "result:<br>";

     print_r($arr_gemerged);

     echo "<br>";

?>



---



so you have to declare array_3 as array() instead of NULL

Aggelos Orfanakos

8 years ago


As with array_merge(), array_merge_recursive() returns NULL in PHP 5 if a non-array parameter is passed to it.

Anonymous

11 years ago


Be careful with array_merge in PHP5.1 not only a E_WARNING is thrown, but also the result is an empty array. So if you merge two select queries and the last one is empty you will end up with no array at all.



<?php

        $array_1 = array('key1'=>'oranges','key2'=>'apples');

        $array_2 = array('key3'=>'pears','key4'=>'tomatoes');

        $array_3 = null;

        $arr_gemerged = array_merge($array_1,$array_2,$array_3);

        print_r($arr_gemerged);

        echo "<br>";

?>



Result on php4:

Array ( [key1] => oranges [key2] => apples [key3] => pears [key4] => tomatoes )



Result on php5:

Warning: array_merge() [function.array-merge]: Argument #3 is not an array in /removed/by/danbrown/for/manual.php on line 7

cyberhorse

11 years ago


clone() is a php function now.

if you create a subclass, it no longer uses samename methods in superclass as a constructor.

kemal djakman

8 years ago


The handling of accessing empty property of a class error has also changed:
<?php

class Foo {

    var $Bar = 'xxx';

    function F() {
        echo $this->$Bar;
    }
}

$Obj = new Foo();
$Obj->F();

?>

Notice the $ sign after object dereference opr?  $Bar is empty inside method F.   PHP4 would only generate a warning, PHP5 throws a fatal error

paul at oconnor-web dot net

8 years ago


The __call function will also lowercase the method arguement:



<?php

   function __call($method, $args) {

     if ($method == 'Foo') {

       return true;

     } else {

       return false

     }

   }

?>



(= false)

Amir Laher

9 years ago


Some other things to be aware of:

some extra strictness:
* object members can no longer be accessed using array-member syntax
* function-calls with too many arguments will now cause errors.

Also, from PHP5.2, custom session handlers are affected:
* Best not to use global objects in custom session-handling functions. These would get destructed *before* the session is written (unless session_write_close() is called explicitly).

dward . maidencreek.com

11 years ago


Another change that we've had problems with while trying to use PHP4 code in PHP5 is how $this is carried across static method calls if they are not declared static in PHP5.  The main issue was that debug_backtrace() now shows the first class with -> instead of the second with :: in the backtrace element when the method in the second class was called statically (using ::) from a method in the first class.

Sinured

8 years ago


Not mentioned above: The PHP/FI 2 function style (old_function aka cfunction) is no longer supported as of PHP 5.

Steven

8 years ago


Three more that we discovered:



== 1. No longer can re-assign $this ==



The follwoing example works under PHP4 (it outputs "OK"), but produces a fatal error under PHP5: 



<?php

  class a 

  { 

    var $text;

    function a() { $this->text = 'OK'; }

  }



  class b

  {

    var $text = 'NOT OK';

    function b() { $this = new a(); }

  }

    

  $myClass = new b();

  echo $myClass->text;

?>



== 2. No comments allowed after shorthand echo block ==



The follwoing example works under PHP4, but produces a sytax error under PHP5.



<?=//comment?>



== 3. Constructors return a reference as default ==



The follwoing example works under PHP4, but produces an E_NOTICE notice under PHP5.



<?php

  class MyClass { function MyClass() { echo('OK'); } }

  $myObj = null;

  $myObj &= new MyClass();

?>



Removing the ampersand solves the problem